The invention relates to an oxidation furnace for the oxidative treatment of fibres, particularly for producing carbon fibres, having    a) a housing which is gastight apart from inlet and outlet regions for the fibres;    b) a process chamber located in the interior of the housing;    c) a blowing device which is arranged in the central region of the process chamber and by means of which hot air can be blown in opposite directions into the process chamber and which comprises a plurality of blowing boxes which are arranged at a vertical spacing above one another and have respective exit openings on opposite sides for the hot air;    d) a respective suction device on both opposite end regions of the process chamber, which extracts hot air from the process chamber;    e) at least one ventilator which circulates the hot air through the blowing device, the process chamber and the two suction devices;    f) at least one heating device located in the flow path of the hot circulated air;    g) guide rollers which guide the fibres in serpentine manner through the clearances between blowing boxes located above one another.
There are various ways of conducting the hot air for treating fibres through an oxidation furnace. Oxidation furnaces which conduct the air according to the “centre-to-end” principle are gaining increasing acceptance. In this, the hot air is blown out in the central region of the process chamber in both directions, that is in the direction of the opposite ends of the process chamber, and extracted again by suction devices at these two ends of the process chamber. The process chamber can also be seen as a zone which can be repeated in the longitudinal direction of the furnace for different temperatures and air flows.
In known oxidation furnaces of the type mentioned at the outset, the blowing boxes forming the blowing device have continuous top and bottom sides and only have exit openings for the hot air at the opposite narrow end faces. This means that hot air does not flow through the clearances between blowing boxes located above one another, in any case not in a defined manner, and the fibres do not undergo oxidative treatment when passing through these clearances. Since the blowing boxes need to have considerable dimensions owing to the air distribution, the stretches in which there is no oxidative treatment of the fibres due to a lack of air flow are by no means insignificant.